Fluoropolymers represent a class of compounds which have notable properties for a large number of applications, from paint or special coatings to leaktight seals, with optics, microelectronics and membrane technology in between. Among these fluoropolymers, copolymers are particularly advantageous because of their diversity, their morphology, their exceptional properties and their versatility.
Most copolymerization reactions carried out in the prior art for preparing fluorinated copolymers are “conventional” free-radical reactions.
For example, the article by Yagi et al., in Polymer Journal 6:429-436 (1979), describes a conventional copolymerization of vinylidene fluoride with trifluoroethylene. These copolymers have particularly advantageous piezoelectric properties, as is discussed in the article by Higashihata et al., in Ferroelectrics 2:85-92 (1981).
The articles by Wang et al., in Macromolecules 39:4268-4271 (2006), by Lu et al., in Macromolecules 39:6962-6968 (2006) and by Zhang et al., in Macromolecules 40:783-785 (2007), describe a process for preparing terpolymers of vinylidene fluoride, trifluoroethylene and chlorotrifluoroethylene by copolymerization of vinylidene fluoride with chlorotrifluoroethylene, followed by reduction of the chlorine atoms of the chlorotrifluoroethylene units.
Moreover, techniques for controlled free-radical copolymerization, i.e. making it possible to obtain control of the molar mass and of the polydispersity index of the polymers, and also synthesis of copolymers with controlled architectures (block, grafted, alternating, gradient, hyperbranched, etc.), have also been proposed.
Document U.S. Pat. No. 6,355,749 describes the preparation of terpolymers of vinylidene fluoride, trifluoroethylene and a comonomer such as chlorotrifluoroethylene or hexafluoropropene, according to a process for controlled copolymerization by means of borane compounds in the presence of oxygen. Likewise, the article by Chung et al., in Macromolecules 35:7678-7684 (2002), describes the production of terpolymers of vinylidene fluoride, trifluoroethylene and a chlorinated comonomer, also according to controlled copolymerization by means of borane compounds. This technique is difficult to implement in practice because of the high cost of the borane compounds and the risk of explosion that they create.
Moreover, it has been possible to prepare some copolymers by methods of free-radical copolymerization controlled by means of xanthate compounds as chain transfer agents, under the name MADIX, for “Macromolecular Design via Interchange of Xanthates”; or else by means of iodinated compounds as chain transfer agents.
Two reviews summarizing relevant works in the field have been published in Macromolecules 43:10163-10184 (2010) and in Chem. Rev. 109:6632-6686 (2009).
The article by Kostov et al., in Macromolecules 44:1841-1855 (2011), describes the production of fluorinated block copolymers using a technique of MADIX type. According to the same strategy, the article by Girard et al., in ACS Macro Letters, 2012, 1, 270-274, reports the synthesis of copolymers based on vinylidene fluoride and on perfluoromethyl vinyl ether.
The article by Liu et al., in Chem. Comm., 47:7839-7841 (2011), provides another example of a xanthate-controlled copolymerization process, concerning copolymers based on chlorotrifluoroethylene and on vinyl ethers exclusively.
The article by Boyer et al., in Journal of Polymer Science A, 47:4710-4722 (2009), describes the synthesis of copolymers of vinylidene fluoride and α-trifluoromethacrylic acid using iodinated compounds as chain transfer agents.
The article by Boyer et al., in Macromolecules 43:3652-3663 (2010), describes the copolymerization of vinylidene fluoride and of perfluoromethyl vinyl ether using iodinated compounds as chain transfer agents. Document US 2009/0105435 describes perfluoromethyl vinyl ether-based diiodinated co-oligomers, according to the same method.
Document WO 01/60869 describes the synthesis of fluorinated elastomers by copolymerization, in an aqueous medium, of VDF with HFP, TFE, CTFE or PAVE (perfluoroalkoxy alkyl vinyl ethers) and of a third comonomer considered to be a monomer with a brominated or iodinated crosslinking site providing subsequent crosslinking.
Finally, document US 2008/0081195 describes terpolymers, such as terpolymers of vinylidene fluoride, trifluoroethylene and chlorotrifluoroethylene, which have two functional end groups and which are prepared by polymerization controlled by borane or diiodinated transfer agents.
However, there is still a need to develop new thermoplastic fluorinated copolymers, in particular by means of controlled free-radical copolymerization methods.
There is quite particularly a need to produce block copolymers based on trifluoroethylene (and in particular based on vinylidene fluoride and on trifluoroethylene) by controlled free-radical copolymerization, more simply and more reliably than in the prior art.
There is also a need to have block copolymers based on trifluoroethylene and in particular based on vinylidene fluoride and on trifluoroethylene, or based on vinylidene fluoride, on trifluoroethylene and on a third comonomer.